1,720,989 research outputs found
Expression of cellular oncogenes: unrearranged c-myc gene but altered promoter usage in radiation-induced thymoma.
No full textExpression of eleven oncogenes was analyzed in thymomas induced by X-rays in the BALB/c strain of mice. H-, K-, N-ras, c-myc, c-myb, and c-abl genes were consistently expressed in thymomas, as well as in normal, age-matched thymus. Only c-myc transcription appeared to be altered in thymomas: a 1.5-3-fold elevated expression of c-myc was found in 42% of the thymomas tested. An altered ratio of two normal promoters, P1 and P2, of the c-myc gene has also been observed in 6 samples out of 15 tested. In one sample, expression from only the P2 promoter was found. A change in DNA sequence to the 5' side of this promoter was detected in an RNAase cleavage assay; this could have disrupted transcription from the P1 promoter. No other structural alteration has been detected within approximately 1800 bases upstream or 700 bases downstream from the 1st exon including exon 1 of the c-myc gene. With the exception of the one sample described, the results of RNAase cleavage assays, as well as Southern blotting of the c-myc gene, show that the structural alteration of this region of c-myc is not generally associated with radiation-induced thymomas in this strain of mice
Abelson murine leukemia virus-induced thymic lymphomas: transformation of a primitive lymphoid precursor.
No full textFor the investigation of whether Abelson murine leukemia virus (A-MuLV) is able to transform in vivo lymphocytes other than those of the B-cell lineage, newborn BALB/c and C57BL/6 mice were given an injection of A-MuLV directly into the thymus. Thymic lymphomas appeared with a short latent period of 4-5 weeks in BALB/c mice and 8 weeks in C57BL/6 mice. Cell lines derived from some thymic lymphomas presented a very immature phenotype and did not express cellular markers of either T-cells (Thy 1.2, Lyt 1.2, and Lyt 2.2) or B-cells (cytoplasmic IgM) even after treatment with several differentiation inducers. Molecular analysis showed that T-cell receptor (TCR) beta chain genes were never rearranged; in one case only, rearrangement of TCR gamma chain genes could be demonstrated, confirming the immaturity of the presumptive T-cell lines studied. Furthermore, the cell lines consistently carried diversity (D)-joining (J) but not variable (V)-D-J rearrangements of the immunoglobulin heavy chain genes. On the whole, these findings suggest that following intrathymic A-MuLV injection neoplastic transformation does involve lymphocytes possibly of T-cell lineage, at a very early stage of differentiation
Increased radiation-induced transformation in C3H/10T1/2 cells after transfer of an exogenous c-myc gene
No full textC3H/10T1/2 cells were infected with a retroviral vector expressing a mouse c-myc oncogene and a drug-selection marker. The resulting cells, morphologically indistinguishable from C3H/10T1/2, displayed a greatly enhanced sensitivity to neoplastic transformation by ionizing radiation or by a chemical carcinogen. Constitutive expression of myc therefore appears to synergize with an initial carcinogenic event, providing a function analogous to a subsequent event that apparently is required for the neoplastic transformation of these cells. This cell system should prove useful in exploring early stages in radiation-induced transformation
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
C-myc gene effects on cell growth and transformation
No full textEpidemiological surveys of occurrence of human neoplastic disease as well as in‐vitro and in‐vivo experimental models indicate that tumorigenesis is a multistep process involving independent genetic events.1‐3 In particular, studies with retroviruses and cloned oncogenes demonstrate that cooperation between oncogenes is required for full transformation of primary embryo cells in culture.4–8 Differences in response to growth factors can be observed between normal cells, which are capable of limited replication and are poorly transformable, and established cell lines, which can be more easily transformed by transfer of cloned oncogenes or exposure to carcinogens.9 Recent reports have provided evidence for effects of some oncogenes at specific points along biochemical pathways that regulate mitosis.10–13 For example, altered expression of the myc gene has been implicated in stimulation of cell growth in response to competence‐inducing growth factors in normal cells and deregulation of cell growth in some neoplastic cells.14–16 Mouse C3H10T1/2 cells have been widely used in in‐vitro transformation studies with chemicals and radiation.17,18 Several lines of evidence are suggestive of more than a single genetic event occurring before cells become able to overgrow the normal monolayer. 19–22 After carcinogenic treatment the appearance of foci of transformed cells is dependent upon proliferation of the initiated cell population, suggesting the requirement for a stochastic event in progression toward a transformed phenotype.23,24 Here we discuss results obtained by introducing the c‐myc coding region via a murine retroviral vector into mouse C3H10T1/2 and rat F2408 cells. We observe that constitutive c‐myc expression promotes growth in semisolid media and enhances responsiveness to PDGF, EGF, FGF, and TGF‐β. Introduction of an exogenous c‐myc gene into C3H10T1/2 does not result in cells that are tumorigenic. However, the expression of an exogenous myc gene increases the tumorigenicity of C3H cells carrying a mutated ras oncogene. We also observed that C3H10T1/2 cells expressing an exogenous myc gene are more efficiently transformed upon radiation or chemical carcinogen treatment. Copyright © 1987, Wiley Blackwell. All rights reserve
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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